Effects of storage conditions of biological materials on the contents of organochlorine compounds and mercury

A study was carried out on the effects of storage conditions on the contents of chlorobiphenyls (CBs), DDT components and mercury (Hg) in biological samples. Wet cod liver and wet plaice muscle tissue were stored in screw-cap jars at −5, −25 and −70°C and a freeze-dried plaice sample was stored in the dark at ambient temperature. Contents of CBs, DDT components and Hg were measured in the samples at 0, 4, 12 and 24 months. Additionally, changes in the matrix were studied by measuring the total and extractable lipid content, dry-weight content, peroxide number, rancidity and by recording HPLC fat fingerprints. Homogeneity was tested by determining the K and Na concentrations in a number of samples. Except for CB118 in wet plaice and Hg in cod liver, no significant changes in the concentrations of CBs, DDT components and Hg were observed. For p,p′-DDT the study was hampered by low levels in the samples. The total lipid determination, using the method of Bligh and Dyer (1959), showed constant results for all storage conditions, whereas extractable lipid contents were affected in wet plaice samples stored at −5 and −25°C. The lower extractable lipid contents coincided with the transformation of triglycerides to fatty acids, found in the lipid fingerprints by HPLC, which suggests that fatty acids are less efficiently extracted by Soxhlet extraction with medium polar solvent mixtures. The peroxide numbers of wet samples at −5 and −25°C demonstrated that oxidation of lipids took place and confirmed deterioration of the matrix. With regard to the determination of CBs and DDE in biological samples, storage at −25°C is sufficient for periods of up to 2 yr. To minimize any effects on the matrix and for storage periods longer than 2 yr it is recommended that the samples should be stored at −70°C or lower.